. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. G9 towards the cicatriculu, near which it' again widens and spreads out like a shallow cone. This whiter internal substance constitutes what has been called the central cavity (or latebra) of the yolk : the whole of this inner part has something of the shape of a flask, with a narrowing neck and a wider mouth at the top, which is, as it were, surmounted or closed in by the cicatricula. (Seey%. 49.) The shape of the yolk, I have said, is not that of a regular ellipsoid ; the less density of the upper part, which is
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. OVUM. G9 towards the cicatriculu, near which it' again widens and spreads out like a shallow cone. This whiter internal substance constitutes what has been called the central cavity (or latebra) of the yolk : the whole of this inner part has something of the shape of a flask, with a narrowing neck and a wider mouth at the top, which is, as it were, surmounted or closed in by the cicatricula. (Seey%. 49.) The shape of the yolk, I have said, is not that of a regular ellipsoid ; the less density of the upper part, which is towards the cica- tricula, giving rise to a widening of the yolk on that side, as may be seen mflg. 44, A, which represents a vertical section of an egg boiled while lying on its side. This does not depend simply on the rising of oil globules in greater quantity to the tipper side of the yolk, but, 'as has already been noticed, on the fixed predominance of globules containing oil in the neighbourhood of the cicatricula. Neither is the outer deeper-coloured por- tion of the yolk altogether uniform in structure or appearance; for it will be seen, both in the raw and boiled egg, but most easily in the latter, that several concentric layers surround the central cavity and canal of the yolk, as well as the funnel-shaped dilatation which lies below the cicatricula. These layers are marked by a slight variation in colour, and are attended by a difference in the minute structure of the corpuscles composing the alternate layers. They probably depend upon the growth of the coloured part of the yolk being more or less rapid at different successive periods. The cicatricula of the newly laid egg is a spot of an opaque yellowish white, easily dis- tinguished by its difference of colour from the rest of the yolk, about one sixth of an, inch in diameter, and lying immediately within the vitelline membrane, in connection at its mar- gins with the most superficial layer of the yolk substance. E
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